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Giant Ragweed (Ambrosia trifida L.)

Also known as great ragweed.

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Giant Ragweed
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An annual plant that is one of the tallest annual plants in North America. Native to a wide range across North America, and common in much of its range. A major allergen, as it produces massive amounts of wind-dispersed pollen.

Range - Expand

Native or Not Present
Native or Expanded
Expanded or Not Present
Native or Expanded or Not Present

This tentative map is based on our own research. It may have limited data on Canada and/or Mexico, and there is some subjectivity in our assignment of plants as introduced vs. expanded. Read more in this blog post.

It is not known exactly where this species is native, but is generally agreed that it is native to Eastern North America and has expanded westward to reach the West Coast, although it is less common in the West. Our treatment loosely reflects BONAP's; some authorities such as POWO mark this species as native the whole way to the West coast but we have not found any evidence supporting this stance. This species also occurs in Canada and Mexico but we have yet to build these portions of its map.


Prefers moist conditions, rich loamy soil, and full sun to light shade.

Found in moist meadows and woodland borders, especially in bottomlands and riparian areas.

Closely related to common ragweed ( Ambrosia artemisiifolia), even though the visual resemblance is not immediately apparent, especially looking only at the leaves. Rarely hybridizes with that species.

Numerous other Ambrosia species, mostly native, occur in North America.

Ambrosia trifida (Giant Ragweed) | Illinois Wildflowers (About This Site)

Ambrosia trifida (Giant Ragweed) | USDA PLANTS Database (About This Site)

Ambrosia trifida | Go Botany (About This Site)

Ambrosia trifida (giant ragweed) | CABI Invasive Species Compendium (About This Site)

Ambrosia trifida | Biota of North America Project (BONAP) (About This Site)

Ambrosia trifida | NatureServe Explorer (About This Site)

Ambrosia trifida | Flora of North America (About This Site)

Ambrosia trifida | Missouri Plants (About This Site)

Great Ragweed | Maryland Biodiversity Project (About This Site)

Ambrosia trifida (Giant Ragweed) | Minnesota Wildflowers (About This Site)

Ambrosia trifida L. | Plants of the World Online (POWO) (About This Site)

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Photo © , CC BY-SA 4.0.